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Fast neutron irradiation tests were performed to determine the correlation of change of drain-source resistance and neutron fluence for power MOSFETs. The Objectives of the tests were: (1) to detect and measure the degradation of critical MOSFET device parameters as a function of neutron fluence (2) to compare the experimental results and the theoretical model. In general, the drain-source resistance increased from 1 Ohm to 100 Ohm after exposure to fast neutron fluence of 3 x 1014 neut/cm2, and decreased by a factor of five after high temperature annealing.

Many high performance amplifiers use power MOSFETs in their output stages, especially in operational amplifier applications whenever high current or power is needed. MOSFETs have advantages over bipolar transistors in amplifier output stage because MOSFETs are majority carrier devices. The result is wide frequency response, fast switching and better linearity than power bipolar transistors. But unlike bipolar circuits, which are relatively tolerant of ionizing radiation, MOSFETs may suffer severe parametric degradation at low total-dose levels. The effects of ionizing radiation on MOSFETs are discussed, and the performance of an amplifier circuit that uses a complementary MOSFET source follower in its output stage is simulated to examine the effect of MOSFET radiation damage on amplifier performance. An increase in power dissipation was the most significant degradation caused by ionizing radiation.

Sorghum (Sorghum bicolor L., Moench) and pearl millet (Pennisetum americanum L., Leeke) were intercropped under soil moisture non-stress and stress at Marana, Arizona during summer 1987. Effects of soil moisture stress and inter-row competition between sorghum and pearl millet on grain yield, 50% bloom, plant height, head length, head exsertion, 1000 grain weight, and number of effective tillers were evaluated. Interplot competition significantly reduced grain yield and head exsertion of peal millet. In sorghum, only plant height was significantly different due to competition. Agronomic characters were significantly different due to the effect of soil moisture stress except head length in pearl millet and head length, 1000 seed weight, and number of effective tillers in sorghum. Sorghum growing in a neighbor plot greatly suppressed millet grain yield under soil moisture stress. Relative yield total of the cereals under intercrop was less than unity under soil moisture stress.

The growth and Nitrogen fixation by one low salt tolerant alfalfa (Medicago sativa L.) and two germination salt tolerant selections inoculated with were investigated at two salt levels (0, -0.6 Mpa) and two N rates (1, 5ppm) using a system which automatically recirculates a nutrient solution. The high level of salinity (-0.6 Mpa osmotic potential of culture solution) resulted in substantial reduction in the N fixation percentage and total fixed N. The effect of salinity was more pronounced for later cuttings than for the earlier cutting. The N fixation percentages were substantially decreased by increasing N level and the reduction was enhanced by time. The N treatment levels did not exhibit a significant effect on total fixed N. Cultivars did not differ in either growth or N fixation. However, the interaction of N and salinity significantly decreased the percentage and amount of N fixation.

Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1995.